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| 2. |
- Abbasi, Saeed, 1973-, et al.
(författare)
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Temperature and Thermoelastic Instability at Tread Braking Using Cast Iron Friction Material
- 2013
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Ingår i: Wear. - : Elsevier BV. - 0043-1648 .- 1873-2577. ; 314:1–2, s. 171-180
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Tidskriftsartikel (refereegranskat)abstract
- Braking events in railway traffic often induce high frictional heating and thermoelastic instability (TEI) at the interfacing surfaces. In the present paper, two approaches are adopted to analyse the thermomechanical interaction in a pin-on-disc experimental study of railway braking materials. In a first part, the thermal problem is studied to find the heat partitioning between pin and disc motivated by the fact that wear mechanisms can be explained with a better understanding of the prevailing thermal conditions. The numerical model is calibrated using the experimental results. In a second part, the frictionally induced thermoelastic instabilities at the pin-disc contact are studied using a numerical method and comparing them with the phenomena observed in the experiments. The effects of temperature on material properties and on material wear are considered. It is found from the thermal analysis that the pin temperature and the heat flux to the pin increase with increasing disc temperatures up to a transition stage. This agrees with the behaviour found in the experiments. Furthermore, the thermoelastic analysis displays calculated pressure and the temperature distributions at the contact interface that are in agreement with the hot spot behaviour observed in the experiments.
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| 3. |
- Abbasi, Saeed, et al.
(författare)
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Temperature and thermoelastic instability of tread braking friction materials
- 2012
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Ingår i: Proceedings 9th International Conference on Contact Mechanics and Wear of Rail/Wheel Systems. ; , s. 606-607
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Konferensbidrag (refereegranskat)abstract
- Braking events in railway traffic often induce high frictional heating and thermoelastic instability (TEI) at the interfacing surfaces. In the present paper, two approaches are adopted to analyse the thermomechanical interaction in a pin-on-disc experimental study of railway braking materials. In a first part, the thermal problem is studied to find the heat partitioning between pin and disc motivated by the fact that wear mechanisms can be explained with a better understanding of the prevailing thermal conditions. The numerical model is calibrated using the experimental results. In a second part, the frictionally induced thermoelastic instabilities (TEI) at the pin-disc contact are studied using a numerical method and comparing them with the phenomena observed in the experiments. The effects of temperature on material properties and on material wear are considered. It is found from the thermal analysis that the pin temperature and the heat flux to the pin increase with increasing disc temperatures up to a transition stage. This agrees with the behaviour found in the experiments. Furthermore, the thermoelastic analysis displays calculated pressure and the temperature distributions at the contact interface that are in agreement with the hot spot behaviour observed in the experiments.
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| 4. |
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| 5. |
- Caprioli, Sara, 1978, et al.
(författare)
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Thermal Cracking of a Railway Wheel Tread due to Tread Braking – Critical Crack Sizes
- 2011
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Ingår i: Proceedings 2011 International Heavy Haul Association Conference. ; , s. 8-
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- A numerical study of tread cracking due to thermal loading induced by tread braking is carried out. The analysis features a computationally efficient approach combining 2D FE-simulations with an analytical evaluation of resulting stress intensity factors. The analysis identifies critical sizes for when existing surface cracks are prone to propagate under thermal loading and resulting crack lengths after propagation. The results imply that fully functional brake systems are not likely to induce thermal crack propagation under normal stop braking, but that with pre-existing defects a severe drag braking due to malfunctioning brakes may cause very deep cracking. Further the analysis concludes the cracking to be a static phenomenon related to the most severe brake cycle, i.e. later brake cycles of similar or lower severity will not cause any significant propagation of existing cracks. Preliminary 3D FE-simulations that have been performed indicate the presented results to be conservative.
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| 6. |
- Caprioli, Sara, 1978, et al.
(författare)
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Thermal cracking of a railway wheel tread due to tread braking -- critical crack sizes and influence of repeated thermal cycles
- 2013
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Ingår i: Proceedings of the Institution of Mechanical Engineers, Part F: Journal of Rail and Rapid Transit. - : SAGE Publications. - 0954-4097 .- 2041-3017. ; 227:1, s. 10-18
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Tidskriftsartikel (refereegranskat)abstract
- A numerical study of tread cracking due to thermal loading induced by tread braking is carried out. The analysis features a computationally efficient approach combining two-dimensional finite-element simulations with an analytical evaluation of resulting stress intensity factors. The analysis identifies critical sizes for when existing surface cracks are prone to propagate under thermal loading and resulting crack lengths after propagation. The results imply that fully functional brake systems are not likely to induce thermal crack propagation under normal stop braking, but that with pre-existing defects, a severe drag braking due to malfunctioning brakes may cause very deep cracking. Furthermore, the analysis concludes the cracking to be a static phenomenon related to the most severe brake cycle, i.e. later brake cycles of similar or lower severity will not cause any significant propagation of existing cracks. Additional three-dimensional finite-element simulations are used to validate the model, and they indicate two-dimensional results to be on the conservative side.
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| 7. |
- Caprioli, Sara, 1978, et al.
(författare)
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Thermal cracking of a railway wheel tread due to tread braking – critical crack sizes and influence of repeated thermal cycles
- 2011
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Ingår i: International Heavy Haul Association Special Technical Session (IHHA STS 2011). ; , s. 8-
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Konferensbidrag (refereegranskat)abstract
- A numerical study of tread cracking due to thermal loading induced by block braking is carried out. The analysis features a computationally efficient approach combining 2D FE-simulations with an analytical evaluation of resulting stress intensity factors. The analysis identifies critical sizes for when existing surface cracks are prone to propagate under thermal loading and resulting crack lengths after propagation. The results imply that fully functional brake systems are not likely to induce thermal crack propagation under normal stop braking, but that with pre-existing defects a severe drag braking due to malfunctioning brakes may cause very deep cracking. Further the analysis concludes the cracking to be a static phenomenon related to the most severe brake cycle, i.e. later brake cycles of similar or lower severity will not cause any significant propagation of existing cracks. Finally it should be noted that preliminary FE-simulations that have been performed indicate the presented results to be conservative.
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| 8. |
- Caprioli, Sara, 1978, et al.
(författare)
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Thermal cracking of railway wheels: Towards experimental validation
- 2016
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Ingår i: Tribology International. - : Elsevier BV. - 0301-679X. ; 94, s. 409-420
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Tidskriftsartikel (refereegranskat)abstract
- Thermal cracking of railway wheel treads is investigated using a combined experimental and numerical approach. Results from controlled brake rig tests of repeated stop braking cycles for a railway wheel in rolling contact with a so-called railwheel are presented. Test conditions are then numerically analysed using finite element (FE) simulations that account for the thermomechanical loading of the wheel tread. For the studied stop braking case, thermal cracks are found in the wheel tread after few brake cycles. Results from thermal imaging reveal a frictionally excited thermoelastic instability phenomenon called "banding" where the contact between brake block and wheel occurs only over a fraction of the block width. This condition results in locally high temperatures. The numerical analysis assesses ratcheting response of the wheel tread material under operational conditions corresponding to two types of banding patterns and also a case of uniform heating. Fatigue life predictions are estimated from the evaluated ratcheting response using a simplified accumulation rule. Predicted lives are found to be in reasonable agreement with experimental results.
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| 9. |
- Caprioli, Sara, 1978, et al.
(författare)
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THERMO-MECHANICAL CRACKING OF RAILWAY WHEEL
- 2011
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Ingår i: Proceedings for Svenska mekanikdagar 2011. ; , s. 1-
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Thermo-mechanical wheel tread damages are common in railway wheels. While the damagemagnitude is limited this is a rather benign phenomenon. However under harsher operationalconditions (winter conditions, poorly tuned damping/suspension, poorly matched wheel–railcontact profiles etc) the extent of the problem may increase dramatically and lead to epidemicsof wheel damages. Since this calls for wheel re-profiling, the result may be extensiveoperational disturbances.The presentation deals with thermo-mechanical damage. In practice one of the failuremodes, thermal cracking or rolling contact fatigue, usually dominates. However, it is mostlikely that the combined thermal and rolling contact loading will have an influence in increasingthe resulting damage as compared to both phenomena acting separately.In the literature there are a multitude of studies on both thermal and rolling contactloading. analyses of the combined load case are however scarce. One major reason for this isthat a combined loading makes a simplification to 2D very cumbersome (not to say futile).Here, a numerical study of the impact of simultaneous thermal and mechanical loading on arailway wheel tread as imposed by braking and rolling contact is presented. 3D finite element(FE) simulations of the thermo-mechanical problem featuring a material model which accountsfor thermal expansion and plastic deformations are carried out. Both pure rolling and tractiverolling are considered. The results indicate a significant influence of the thermal loading onthe resulting stress/strain response also in cases of relatively moderate temperature increases.In particular, a combination of thermal loading and high traction rolling is found to be verydetrimental.The resulting damage of the wheel tread is manifested by the formation of small surfacecracks. In cases of high thermal loading, these cracks will evolve to deep radial cracks thatcan, in a worst-case scenario, cause catastrophic wheel failures. Since this is a potential safetyproblem it is important to understand the driving mechanisms behind these cracks.To this end, a numerical study of thermal cracking of a wheel subjected to high thermalloading was carried out. The analysis features a computationally efficient approach where2D FE stress analysis owing to thermal loading during braking and subsequent cooling iscombined with an analytical evaluation of resulting stress intensity factors of a radially orientedsurface crack in the wheel tread. The analysis identifies critical sizes for when existingsurface cracks are prone to propagate under thermal loading and resulting crack lengths afterpropagation. The results imply that fully functional brake systems are not likely to inducethermal crack propagation under normal stop braking, but that with pre-existing defects asevere drag braking due to malfunctioning brakes may cause very deep cracking. Further theanalysis concludes the thermal cracking to be a (more or less) static phenomenon related tothe most severe brake cycle. In other words: later brake cycles of similar or lower severitywill not cause any significant propagation of existing cracks. To further validate the analysisof the semi-analytical analysis, preliminary 3D FE-simulations have been performed.
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